Innovative small-scale testing to investigate thermo-mechanical damage in tread-braked railway wheel steel paired with various types of cast iron

Abstract

This study investigates the thermo-mechanical damage to wheel steel caused by the use of different types of grey cast iron as brake materials. Both untreated and austempered specimens of cast iron were tested to evaluate their wear behaviour and frictional properties under controlled conditions employing an innovative small-scale testing rig called “4-contact machine”. The experiments measured temperature on the specimens' contact surface, wear, friction coefficient and power developed. An in-depth metallographic analysis of all wheel samples was also conducted to determine the impact on wheel steel integrity. Significant findings include the formation of a martensitic transfer layer on the wheel samples’ surface, resulting from the high temperature and pressure during braking. This layer, being harder than the unaltered wheel steel, highlights the thermo-mechanical stress imposed on the wheel. Austempered cast iron brake samples showed superior performance with reduced wear and lower friction coefficients compared to untreated samples. The results emphasize the need for improved brake materials to mitigate thermo-mechanical damage to wheels, enhancing both safety and longevity of railway brake systems. This research contributes to the development of more resilient brake materials, providing valuable insights for the railway industry in optimizing material selection for enhanced operational efficiency and reduced maintenance costs. These advantages are particularly notable compared to composite materials, as austempered cast iron offers comparable or superior performance without the higher costs or vehicle modifications required for composites, all while maintaining its eco-friendly nature.